The present disclosure is directed to a fluid operated fishing tool and more particularly to one which has a soft contact or a soft set tool. It is especially adapted for use in grasping and holding a fish (an item to be retrieved) which does not necessarily have an easily gripped upper end such as a drilling motor stem. It will be discussed in the context of retrieving a typical elongate cylindrical device that may have a smooth upper end, and particularly one which does not have a spear head, or indeed, a fish of any shape.
The fishing tool of the present disclosure is a type of retrieval tool or overshot which reaches around and grasps the fish. It is constructed with a soft set or soft touch mechanism. The soft set mechanism is especially desirable in light of the varied size and shape of the upper end of the fish. The shape of the fish may be known, but in some instances, it is completely unknown. Likely, it will be an elongate device having no particular anticipated shape. Whatever the case, the present device is constructed to reach over the fish and surround the upper end of the fish. The fish can be shredded, twisted, bent, or otherwise parted. It can just as easily be an elongate cylindrical member which simply has no shoulders, no threads, no undercut shoulder, no serrations or knurled surface, etc. It can be smooth metal or rough with no limit. This soft set structure reaches over the fish and conforms to the fish regardless of its shape. The fish is gripped by a surrounding resilient sleeve which is on the interior of the present overshot device. This sleeve fits around the fish with some clearance. The sleeve is on the interior of a cylindrical housing. By the proper actuation of the present device, fluid pressure is applied behind the sleeve so that the sleeve expands radially. It expands inwardly to grasp the fish which is enclosed within the sleeve. The upper end of the sleeve is free floating on a sealed surface of a stem which construction allows the sleeve to contract. The sleeve floats to enable it to conform to the fish. By having the top free floating, the sleeve material is in compressed when a pull is exerted. This allows for more strength in the tool. Also, the weight of the fish tends to help set the sleeve when coming out of the hole. While the present apparatus is able to transfer a tremendous amount of pulling force to the fish, there is the possibility that the fish will not break free. In that instance, it is then desirable that the fish be released. The present apparatus includes a mechanism by which release is accomplished. The soft set tool is set by pumping incompressible fluid behind the sleeve. That space is later evacuated of high pressure fluid and the pressure is released by dropping a ball to seat on a pinned sleeve. A predetermined pressure will shear the pins and move the sleeve downward to open access ports to the pressure chamber. The same movement opens ports to the annular area to eliminate the problems of pulling a wet string. This enables release of the fish and permits relaxation of the sleeve. In that instance, the sleeve will relax and expand radially outwardly for restoration to its original shape, and thereby release the fish. This makes retrieval of the fishing tool something easily done when the fish cannot be readily moved.
In very general terms, the tool of the present disclosure threads to a tubing string which enables the tool to be lowered in a well where a fishing job is to be conducted, and extend over the fish. The tool incorporates an elongate cylindrical upper end which has two internal sleeves which are selectively plugged by dropping a specifically sized ball in the tubing string. Dropping the smaller ball initiates seating on the lower sleeve, shutting off circulation thru the tool and allowing a predetermined pressure to be applied in the pressure chamber to set the soft set grapple. The same pressure will shear the sleeve pins. This allows the sleeve to move downwardly to open ports to the annular area, thereby establishing circulation. The setting pressure is retained in the setting chamber by back pressure valves. This ball stops flow axially of the tool and diverts the flow into a passage in the sidewall. This passage is ordinarily closed when flow is axially through the tool, closure being accomplished by a spring actuated check valve. When the check valve is overpowered, it delivers fluid under pressure controlled at the wellhead so that pressure build-up occurs in a chamber within the tool. The chamber is concentric around and coextensive along a resilient sleeve which is forced to shrink radially inwardly by the surrounding fluid pressure. This pressure causes the resilient material of the sleeve to conform against the surface of the fish and to grasp the fish so that it is held. As will be detailed substantially with the development of the present disclosure, the fish is held so that axial pulling can occur, hopefully retrieving the fish in the fashion of an overshot retrieval too. In the event that the procedure requires later release of the fish, a larger ball is dropped in the tubing string and lands on a larger bore seat at the upper end of the tool. By increasing pump pressure at the wellhead, this sphere in conjunction with a moveable sleeve is moved downwardly, breaking a set of shear pins. When it moves, the sleeve closes off or blocks the lateral passage by which fluid is introduced around the sleeve. Moreover, this enables a passage to be actuated which voids the chamber around the sleeve so that any build-up of pressure in that area is relieved. This permits the sleeve then to relax. Moreover, the downward movement opens a passage above the ball seat to establish circulation. This eliminates the necessity of pulling a wet string, reducing mud spillage. In this type of operation, the tool also has fill-up valves at the bottom of the tool and air release valves at the top. Both of these valves close when adequate pressure is achieved in the setting chamber.
An important additional aspect for accomplishing the soft grab is changing the pressure chamber from around the grasp sleeve pressure cylinder above the soft grasp sleeve with a piston which, when pressure is achieved is applied, will compress the soft sleeve, thus conforming it to the fish shape. In this mechanism, the bottom fill up valves are replaced by drain holes in the outer sleeve. This is necessary to void any fluid contained behind the soft grasp sleeve to allow complete sleeve compression around the fish. It is also necessary to adapt a piston to seal off on the outer sleeve to effect the compression force.